Systems and methods to reduce sensor interference associated with electrical therapies

ABSTRACT

Methods and systems for reducing interference in a therapeutic energy delivery system by delivering an electrical therapeutic signal to a patient to provide a therapeutic benefit to the patient, and delivering an electrical counter signal to the patient that destructively interferes with an electrical interference signal resulting from delivering the electrical therapeutic signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of U.S. Prov. App. No. 61/801,002,filed Mar. 15, 2013, the disclosure of which is incorporated herein byreference.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

BACKGROUND OF THE INVENTION

Neuromuscular electrical stimulation (NMES) (also referred to as poweredmuscle stimulation, functional muscle stimulation, electrical musclestimulation, electrical stimulation, and other terms) is an establishedtechnology with many therapeutic uses, including pain relief, preventionor retardation of disuse atrophy, and improvement of local bloodcirculation. NMES is typically delivered as an intermittent andrepeating series of short electrical pulses. In many implementations,these pulses are delivered transcutaneously by surface electrodes thatare attached to a person's skin. Electrodes may be held to the skinthrough the use of straps, adhesives, or other mechanisms, and oftencontain a coupling layer composed of hydrogel that is capable ofenhancing the efficiency of energy transfer from the electrode to theskin and underlying tissues.

A group of persons who could potentially show large benefit from NMEStherapy are those who are being monitored medically for other conditionsor as a standard part of their medical care. For example, many patientsin the hospital are subjected to long periods of bed rest and developatrophy that NMES could prevent. During hospitalization these patientsare often connected to cardiac and other electrical monitors (ex. ECG)that measure/track certain aspects of the patient's health (for example,assessing potential arrhythmia and calculating heart rate). Similarstatements may be made about subjects who might use NMES in otherclinical settings or at home—electrical monitoring is often an importantpart of a patient's care that may drive either diagnostics or anintervention. Monitoring equipment may be external and temporary (ex.Holter monitor) or may be part of an implanted device that is permanentor semi-permanent. Monitoring and sensing capabilities may bestand-alone or integrated into another piece of medical equipment ordevice.

As NMES delivers electrical impulses to the body during its therapeuticapplication, there is the potential for interference with electricalmonitoring equipment. For example, electrical signals delivered to thebody as part of NMES treatment may be detected by sensors associatedwith other equipment, even in areas of the body remote to the site ofNMES application. These NMES signals may alter or combine with (forexample, through constructive or destructive interference) thephysiological signals the sensors are intended to measure. If ofsufficient amplitude, this interference may mask or alter signalsdetected by sensors in such a way that these signals are no longerreflective of the physiological event intended to be monitored.Accordingly, dangerous conditions may arise where a critical clinicalevent is not detected (for example, a cardiac arrhythmia goesundetected) or a device that implements sensing/monitoring behaves in anundesired fashion (for example, an implanted defibrillator shocks thepatient during normal cardiac function because sensor interference isinterpreted as a critical arrhythmia).

It is important to distinguish the situation currently described fromthe case of external electrical noise or other forms of external noiseinterfering with sensors. Sources of potential monitor interferencearising from outside of the body are well-understood, and appropriatemechanisms are well-known in the art to prevent or limit substantialdeleterious effects associated with these sources of noise. Thepresently-described situation, where sensor/monitor interference arisesdue to an electrical signal injected into or otherwise applied to thebody, is much more challenging to handle and has limited availablesolutions.

The prior art illustrates some attempts to solve the interferenceproblem described herein, but solutions described have inherentpractical limitations. Solutions described in the prior art often usehardware or software-based signal filters that are applied to noisy datacollected by sensors. Depending on the characteristics of both thedesired and the interfering signals, these filters may be successful atremoving the interference signal or minimizing its impact, allowingmonitors and devices to function normally. Other solutions known in theart involve the use of additional sensors that are used in conjunctionwith the primary sensors associated with the monitor or device. Theseadditional sensors may detect the interference signal, or a differentcombination of the desired and interference signals, and can be combinedwith data from the primary sensors in order to eliminate or minimize theimpact of the interference signal on monitoring or sensing. For example,some systems described in the art use secondary sensors to measure theinterference signal applied to the body, then subtract secondary sensordata from primary sensor data (which measures a combination of thedesired physiological signal and the interference signal applied to thebody) to minimize residual interference. Similar systems combinesignals, sometimes from many additional sensors, in different ways (withor without the use of signal filters) to achieve similar goals.

The prior art systems noted above have practical limitations related totheir implementation in the real-world. For example, to use filteringtechniques to limit the impact of interference signals applied to thebody, one would need access to sensor data following its detection butbefore it is interpreted, displayed, or otherwise used byalgorithms/components later in a monitoring or device system's process.As a result, filters can be employed by the original manufacturers ofmonitoring equipment, but third-parties trying to prevent interferencewith existing equipment/monitors/sensors are prevented from implementingnew filters as they generally do not have the proper access to makehardware or software modifications to existing equipment. Similarlimitations are associated with a multiple-sensor approach; even incases where the use of multiple sensors could help eliminateinterference with measurements of physiological signals, these sensorscannot generally be added post-market to existing monitors or devicesthat measure and interpret data.

As one specific example, take the case of a patient in a hospital havinghis cardiac signals monitored with standard ECG equipment. ECG signalsare measured by sensors (ECG electrodes) applied to the body and relayedto a processor/display unit via conventional leads that are well-known.If NMES is applied to the patient, signals detected by ECG electrodesmay be a blend of the cardiac signals desired to be measured and aninterference electrical signal produced as a byproduct of NMEStreatment. Even if the NMES interference signal could be isolated andmeasured exactly with secondary sensors, there is no way to adjust theECG electrode data with information from the secondary sensors withoutmajor modifications to the ECG monitoring system. In other words, theECG sensor data is ported directly to the processer/display unit, andthere is no practical way to intercept this data and adjust it usinginformation from a secondary sensor before it is interpreted anddisplayed. Similar limitations are associated with the use of the filterapproach. Thus, there is no way to prevent this type of signalinterference using these methods without working directly with the ECGmonitor manufacturer to implement them. As there are a vast possibilityof devices and monitors that could suffer from interference from NMESdevices and other devices that supply electrical signals to the body,collaborating with each manufacturer to implement to the techniquesdescribed in the prior art is impractical and thus these solutionsaren't feasible for widespread use.

Novel solutions are needed to allow NMES and other devices to be usedsafely in the presence of monitoring and sensing equipment. These newapproaches must solve the practical problems described above, and allowfor interference reduction to be implemented in such a way that nomodifications to monitoring devices are needed in order to reduce theinterference produced by the therapy devices and subsequently detectedby the sensors on the monitoring devices. Disclosed within are devices,systems, and methods for achieving these goals.

SUMMARY OF THE INVENTION

Detailed within are devices, systems, and methods for reducing theinterference that electrically-based systems or therapies may produce inmonitoring systems or devices that involve sensing electrical signals.Several embodiments and implementations of the invention are describedherein, though it will be evident to those skilled in the art that theseare exemplary and that numerous configurations of the present inventionare possible. An important aspect of many of the embodiments of thepresent invention is that interference is reduced by preventing orlimiting interference signals from reaching primary sensors associatedwith monitoring system or device sensors. As opposed to methods andsystems described in the prior art, which use filters or secondarysensors to try to remove interference components from a combinationsignal (comprised of both desired and interference signal components)detected by primary sensors, the present invention seeks to preventthese interference components from reaching the primary sensor in thefirst place. Accordingly, no modifications of existing monitoringsystems or devices is required in order to reduce or eliminate theimpact of interference signals on the ability for these systems ordevices to measure their target physiological signals. While much ofthis disclosure is written using the modality of NMES as an illustrativeexample, it will be obvious to those skilled in the art that with minormodifications the methods, devices, and systems described herein may beapplied with utility to other energy-delivery therapies as well.Similarly, while interference with ECG monitoring will be used as anexample, this should not be construed as limiting as the same inventionsmay be applied to minimize interference with other types of monitoringand/or devices. It should be appreciated that different aspects of theinvention can be appreciated individually, collectively, or incombination with each other.

In a preferable embodiment, an NMES system is configured with multipleindependent energy-delivery channels. One or more of these channels isused to apply NMES therapy to a body part. A by-product of thisapplication of NMES energy is an interference signal that could inhibitthe function of devices elsewhere on or in the body that monitor orsense electrical signals. To address this problem, other channels in theNMES system may be used to provide a counter signal which can interactand destructively interfere with the interference signal produced by thestandard NMES waveforms. This counter signal has an amplitude and aphase such that, at monitoring locations remote to the site of NMEStherapy, the interference signal produced by NMES energy delivery iseliminated or minimized. Some embodiments may have more energy channelsdedicated to apply NMES to a body part than energy channels used tocancel the NMES interference signal remotely. This active cancellationapproach is differentiated from the prior art because interferencesignals are addressed prior to them reaching the primary sensorassociated with monitoring devices or other equipment—no alterationsneed to be made to existing equipment.

In preferable embodiments of the invention, the amplitude, phase, shape,and other properties of the counter signal may be adjusted by a user toachieve optimal results. In variation embodiments, the counter signal isfixed or adjusted automatically based on settings of the NMES device. Inpreferable embodiments, the electrodes used to deliver the countersignal to the body are located in a fixed location relative to thestimulation electrodes used to deliver NMES energy to the body. Invariations of the preferable embodiments, the electrodes delivering thecounter electrode signals may have adjustable locations relative to theregion of NMES therapy.

In a variation of the preferable embodiment, sensors are integrated intothe NMES system that measure the interference signals produced by theNMES treatment. In some embodiments, this measurement occurs remotelyfrom the region being treated with NMES, while in some embodiments thesensing/measurement occurs locally. After sensors have measured thesignal produced by NMES, internal systems are used to adjust andfine-tune the counter signals that are produced by the system in orderto limit or eliminate interference with monitoring equipment or sensingdevices.

In some embodiments, multiple independent energy delivery channels areused to produce the counter signal. In this embodiment, each independentenergy channel may be configured to deliver energy to separate pairs orgroups of electrodes, so that the counter signal may take on numerousshapes and properties. In other variations of a preferable embodiment, asingle energy delivery channel interfacing with a single pair ofskin-contact electrodes is used to provide to the counter signal to thebody. In further variations, a monopolar configuration is implementedthat uses a single electrode contact site to provide the desired countersignal.

An important aspect of preferable embodiments of the invention is thatenergy delivered to produce the counter signal does not interfere withor degrade the ability to successfully treat a patient or subject withNMES. In other words, the counter signal can effectively cancel the NMESinterference signal at remote sensing locations but does not degrade theNMES electrical signal used to create muscle contraction in the regionbeing treated with NMES. Any viable solution to the problems describedherein must allow both the NMES system (or another energy-relatedtherapy that is being applied) and the monitoring/sensing system to beused normally and effectively simultaneously.

The disclosed devices, methods, and systems are useful because they willenable effective NMES therapy in a subset of persons that currently maynot qualify for it due to reliance on monitoring systems or devices. Forexample, the United States FDA currently requires device labeling forNMES systems indicating that they should not be used on patients withcardiac pacemakers or defibrillators, as there is a fear of theconsequences of interference with the sensing systems in these devices.Novel devices, systems, and methods that could prevent interference withthe sensing systems of cardiac devices would allow NMES therapy to reacha much larger group of patients who could benefit from the treatment.The presently-disclosed inventions will also allow NMES to be used moresafely in hospital settings, particularly those settings which requirepatients to be connected to ECG or other monitoring systemscontinuously.

One aspect of the disclosure is a muscle stimulation system comprising astimulation electrode configured to be secured to a patient to deliveran electrical muscle stimulation signal to the patient; and an countersignal electrode configured to be secured to the patient and relative tothe stimulation electrode to deliver an electrical counter signal to thepatient; and at least one controller adapted to generate the electricalmuscle stimulation signal and the counter signal, wherein the electricalcounter signal is adapted to destructively interfere with an electricalinterference signal resulting from the electrical muscle stimulationsignal.

In some embodiments the electrical counter signal is adapted such thatit does not degrade the stimulating effect of the electrical musclestimulation signal.

In some embodiments the electrical counter signal is adapted to minimizeor eliminate the interference signal.

In some embodiments the electrical counter signal has an oppositepolarity and substantially the same amplitude as the interferencesignal.

In some embodiments the electrical counter signal has an amplitude thatis less than an amplitude of the electrical muscle stimulation signal.

In some embodiments the electrical counter signal has a shape that isdifferent than a shape of the electrical muscle stimulation signal.

In some embodiments the at least one controller is adapted so that theelectrical counter signal is fixed.

In some embodiments the at least one controller is adapted such that theelectrical counter signal can be manually or automatically varied. Theat least one controller can be adapted such that at least one of anamplitude, a phase, and a shape of the electrical counter signal can bemanually or automatically varied. The at least one controller can beadapted to vary the electrical counter signal based on the electricalinterference signal. The system can further include an interferencesignal sensor configured to be secured to the patient and to sense theelectrical interference signal.

In some embodiments the system also includes an interference sensorconfigured to be secured to the patient and adapted to sense theinterference signal at a location different than where the electricalmuscle stimulation signal is delivered to the patient, wherein theelectrical counter signal is based on the sensed interference signal.

In some embodiments the electrical counter signal is adapted to reduceinterference between a sensed physiological signal from the patient andthe interference signal. The physiological signal from the patient canbe an EKG signal.

In some embodiments the system further comprises a pad configured to bepositioned on the patient and comprises the stimulation electrode andthe counter signal electrode. The pad can further comprise aninterference sensor adapted to sense the electrical interference signal.The interference sensor can be disposed between the stimulationelectrode and the counter electrode. The counter electrode can bedisposed between the stimulation electrode and the interference sensor.

One aspect of the disclosure is a method of reducing interference in amuscle stimulation system comprising delivering an electrical musclestimulation signal to a patient to stimulate muscle contraction; anddelivering an electrical counter signal to the patient thatdestructively interferes with an interference signal resulting fromdelivering the electrical muscle stimulation signal.

In some embodiments delivering the electrical counter signal does notdegrade the stimulating effect of the delivered electrical musclestimulation signal.

In some embodiments delivering the electrical counter signal minimizesor eliminates the interference signal.

In some embodiments delivering the electrical counter signal comprisesdelivering an electrical counter signal that has an opposite polarityand substantially the same amplitude as the interference signal.Delivering the electrical counter signal can include delivering anelectrical counter signal that has an amplitude less than an amplitudeof the delivered electrical stimulation signal.

In some embodiments delivering the electrical counter signal comprisesdelivering an electrical counter signal that has a shape that isdifferent than a shape of the electrical muscle stimulation signal.

In some embodiments the method further comprises modifying a parameterof the delivered electrical counter signal and delivering a secondelectrical counter signal with the modified parameter. Modifying aparameter of the delivered electrical counter signal can includemodifying at least one of an amplitude, a phase, and a shape of thedelivered electrical counter signal. Modifying a parameter of thedelivered electrical counter signal can be in response to sensing theinterference signal with an interference signal sensor.

In some embodiments the method further comprises sensing theinterference signal with an interference signal sensor. Sensing theinterference signal with an interference signal sensor can comprisesensing the interference signal at a location different than where themuscle stimulation signal is delivered to the patient and where thecounter signal is delivered to the patient. Sensing the interferencesignal with an interference signal sensor can comprise sensing theinterference signal at a location between where the muscle stimulationsignal is delivered to the patient and where the counter signal isdelivered to the patient.

In some embodiments delivering an electrical counter signal is inresponse to sensing the interference signal.

In some embodiments the method further comprises sensing a physiologicalsignal from the patient, and wherein delivering the counter signalreduces interference between the sensed physiological signal and theinterference signal. Sensing a physiological signal from the patient cancomprise sensing an EKG signal from the patient, and delivering thecounter signal can reduce interference between the EKG signal and theinterference signal.

One aspect of the disclosure is a therapeutic energy delivery systemcomprising a therapeutic energy delivery element configured to besecured to a patient to deliver therapeutic energy to the patient; acounter energy delivery element configured to be secured to the patientand relative to the therapeutic energy element to deliver counter energyto the patient; and at least one controller adapted to generate thetherapeutic energy and the counter energy, wherein the counter energy isadapted to destructively interfere with interference energy resultingfrom the therapeutic energy.

In some embodiments the counter energy is adapted such that it does notdegrade the therapeutic effect of the therapeutic energy.

In some embodiments the counter energy is adapted to minimize oreliminate the interference energy.

In some embodiments the therapeutic energy is an electrical signal, thecounter energy is an electrical signal, and the interference energy isan electrical signal. The counter signal can have an opposite polarityand substantially the same amplitude as the interference signal. Thecounter signal can have an amplitude that is less than an amplitude ofthe therapeutic signal. The counter signal can have a shape that isdifferent than a shape of the therapeutic signal. The at least onecontroller can be adapted such that at least one of an amplitude, aphase, and a shape of the counter signal can be manually orautomatically varied. The at least one controller can be adapted to varythe counter signal based on the interference signal.

In some embodiments the at least one controller is adapted such that thecounter energy can be manually or automatically varied.

In some embodiments the system further comprises an interference sensorconfigured to be secured to the patient and adapted to sense theinterference energy at a location different than where the therapeuticenergy is delivered to the patient, wherein the counter energy is basedon the sensed interference energy.

In some embodiments the counter energy is adapted to reduce interferencebetween sensed physiological energy from the patient and theinterference energy. The sensed physiological energy from the patientcan be an EKG signal. The system can further include a sensor adapted tobe secured to the patient at a location relative the therapeutic energyelement and configured to sense the physiological energy from thepatient.

One aspect of the disclosure is a method of reducing interference in atherapeutic energy delivery system comprising delivering an electricaltherapeutic signal to a patient to provide a therapeutic benefit to thepatient; and delivering an electrical counter signal to the patient thatdestructively interferes with an electrical interference signalresulting from delivering the electrical therapeutic signal.

In some embodiments delivering the electrical counter signal does notdegrade the therapeutic effect of the delivered electrical therapeuticsignal.

In some embodiments delivering the electrical counter signal minimizesor eliminates the interference signal.

In some embodiments delivering the electrical counter signal comprisesdelivering an electrical counter signal that has an opposite polarityand substantially the same amplitude as the interference signal.Delivering the electrical counter signal can comprise delivering anelectrical counter signal that has an amplitude less than an amplitudeof the delivered electrical therapeutic signal.

In some embodiments delivering the electrical counter signal comprisesdelivering an electrical counter signal that has a shape that isdifferent than a shape of the electrical therapeutic signal.

In some embodiments the method further comprises modifying a parameterof the delivered electrical counter signal and delivering a secondelectrical counter signal with the modified parameter. Modifying aparameter of the delivered electrical counter signal can comprisemodifying at least one of an amplitude, a phase, and a shape of thedelivered electrical counter signal. Modifying a parameter of thedelivered electrical counter signal can be in response to sensing theinterference signal with an interference signal sensor.

In some embodiments the method further comprises sensing theinterference signal with an interference signal sensor. Delivering anelectrical counter signal can be in response to sensing the interferencesignal. Sensing the interference signal with an interference signalsensor can comprise sensing the interference signal at a locationdifferent than where the therapeutic signal is delivered to the patientand where the counter signal is delivered to the patient. Sensing theinterference signal with an interference signal sensor can comprisesensing the interference signal at a location between where thetherapeutic signal is delivered to the patient and where the countersignal is delivered to the patient.

In some embodiments the method further comprises sensing a physiologicalsignal from the patient, and wherein delivering the counter signalreduces interference between the sensed physiological signal and theinterference signal. Sensing a physiological signal from the patient cancomprise sensing an EKG signal from the patient, and delivering thecounter signal reduces interference between the EKG signal and theinterference signal.

BRIEF SUMMARY OF THE DRAWINGS

As shown in FIG. 1, an embodiment of the systems and devices describedherein that demonstrates the main system components.

As shown in FIG. 2, variations of preferable embodiments of the devicesand systems that include electrodes used to deliver NMES and electrodesused to produce a counter signal.

As shown in FIG. 3, various electrical signals associated with thedevices, systems, and methods described herein.

As shown in FIG. 4, variations of preferable embodiments of the devicesand systems that include electrodes used to deliver NMES and electrodesused to produce a counter signal as well as sensors used in conjunctionwith the system.

As shown in FIG. 5, variation embodiments of the devices and systemsshown in multiple configurations.

As shown in FIG. 6, several steps in one preferable embodiment of themethod described herein.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides methods, devices, and systems for limiting theimpact electrical-based therapies may have on monitoring systems and/orother devices that require sensing of electrical signals. Though thisdisclosure uses the modality of NMES as an illustrative example, thoseskilled in the art will appreciate that the presently-disclosedinvention may be applied with utility to other energy-delivery therapiesas well. Various aspects of the invention described herein may beapplied to any of the particular applications set forth below or for anyother types of electrical stimulation and sensing systems or methods.The invention may be applied as a standalone device, or as part of anintegrated medical treatment system. It shall be understood thatdifferent aspects of the invention can be appreciated individually,collectively, or in combination with each other.

With reference to FIG. 1, in a preferable embodiment, the systemincludes three core components: surface electrodes that are used tocouple electrical energy into and out of the body (104, 105), astimulation control unit (101) that creates the stimulation energy andpotentially other electrical pulses and delivers them to the surfaceelectrodes, and a wired connection (102) to allow communication betweenthe electrodes and control unit. In some variation embodiments, awireless system using may be used that eliminates the need for a wiredconnection, instead using a radiofrequency transmission, optical,acoustic, or electromagnetic signals, or another suitable mechanism. Ina preferable embodiment, the electrodes will be assembled into a custompad (103) such that electrode layout and configuration will bepre-optimized for a particular region of the body. Some electrodes maybe pre-designated to deliver stimulation energy that delivers NMEStherapy (104), while others may be configured to produce counter signals(105) intended to prevent the NMES therapy from creating meaningfulinterference in remote sensors that are intended to measureelectrophysiological signals. In some embodiments, electrodes may beused both to deliver NMES therapy and to deliver counter signals, and/ormay be designated by the user or control unit to produce one type ofsignal or the other at the time of NMES treatment. The control unit is aseparate unit that may be located some distance from the personreceiving therapy. In an alternate embodiment, the control unit may beintegrated into a housing unit containing the stimulating electrodes, orin another way be adapted to reside proximate to the region of NMES.

In a preferable embodiment, the control unit contains components such asa signal generator, memory, processor, and power supply. The primaryoperation of the control unit may be provided by a microprocessor, fieldprogrammable gate array (FPGA), application specific integrated circuit,some combination of these mechanisms, or other suitable mechanism.Electrical transformers or another suitable mechanism is used to produceelectrical energy pulses that may be delivered to the body of a subject.When activated, the control unit generates electrical signals that aretransmitted to the surface electrodes in the pad, which couple theenergy into the body (for example, to activate muscles). Some electricalstimulation parameters, including the duration of therapy, areadjustable by the operator through buttons, knobs, dials, or switches onthe control unit. Other electrical stimulation parameters, such asstimulation pulse energy amplitude, may be adjusted by the user throughcontrol unit controls or be automatically optimized using automaticalgorithms implemented by the control unit. The control unit may alsocontain items such as a touchscreen or other form of display and/or userinterface, data acquisition channels and associated hardware/software,and other safety-control features.

In a preferable embodiment, the control unit is capable of transmittingelectrical pulses on at least one and preferably many more (ex. 6-12)channels simultaneously and independently. In some embodiments, thecontrol unit may also be capable of creating arbitrary phase delaysbetween pulses originating from different channels. In variations ofthese embodiments, the control unit may transmit pulses on some channelsdependently and others on different channels independently.

In a preferable embodiment, the system electrodes are arranged on a padin an array with a predetermined layout (see, for example, FIG. 1( b)).In a preferable embodiment, the pads are comprised of a thin andflexible housing with an adhesive backing to facilitate maintenance ofskin contact with the person receiving NMES. More than one adhesivematerial may be used; for example electrode contact areas may use ahydrogel or similar backing while other pad areas may be secured with amore gentle adhesive (ex. those used in bandages). The hydrogel backingfor electrodes will also enhance the coupling of electrical energy andsignals between stimulation electrodes and the person's body. The padcontains two or more strategically-placed surface electrodes that areused to deliver electrical energy to muscles and/or nerves in order toproduce muscle contraction, as well as one or more electrodes used toproduce a counter signal. In variation embodiments, electrodes may bediscretely-placed in contact with tissue independent of a larger pad (asin FIG. 2( d)). In some embodiments, a system pad may also contain asmall and lightweight control unit that is intended to sit proximate tothe region of tissue being treated. In some embodiments, more than onepad may be used, with each pad containing at least one electrode thatproduces either a stimulating or counter signal.

In preferable embodiments the system will be configured specifically fora particular region of the body intended to receive NMES. Referring toFIG. 2, a system is shown configured for use with muscle stimulation ofthe left quadriceps. A control unit (202) is shown to connect to a padcontaining electrodes (203) through a wired connection. Also shown arecommon locations for ECG electrodes (204) which are used to monitor thesubject's cardiac activity. In preferable embodiments of the system,electrodes used to deliver the counter signal to the body will liebetween the monitoring system sensors and the electrodes used to deliverNMES therapy. In the example shown, the counter-signal electrodes thuslie between the quadriceps and the torso. In FIG. 2( b), a detailed viewof one embodiment of a system pad (203) is shown, with example locationsof stimulation electrodes (2044) and electrodes used to deliver thecounter signal (205). Note the counter signal electrodes would fallbetween the NMES electrodes and the ECG measuring electrodes of themonitoring system. A different implementation of this embodiment isshown in FIG. 2( c), where the counter signal electrodes are arrangeddifferently relative to the stimulation electrodes, primarily becausethe pad (206) has been configured to deliver therapy to a differentanatomical location (for example, the back). In FIG. 2( d), anembodiment of the system is shown where no pad is used; both types ofelectrodes are placed discretely on the skin at locations of theoperator's choosing, and are not fixed in position relative to oneanother.

During the process of NMES, electrical energy is generally deliveredbetween at least two electrodes in a set. The bulk of electrical energytravels between the electrodes in the set, though fields of energyspread away from the stimulation region. It is these fields which cancreate interference problems for monitoring in remote regions. Anexample is provided in FIG. 3. In (a), a sample signal produced by thecontrol unit is shown (x-axis is time, y-axis is voltage, not to scale).This is one example of an asymmetric, biphasic square wave commonly usedin NMES. In FIG. 3( b), an example signal that can be measured justoutside the region of stimulation (in the area marked as (1) in FIG. 3(e)) is shown. The overall energy amplitude is lower (not to scale), andthe shape is somewhat different than the original signal shown in (a).However, the pulse width and the polarity may be similar. In (c), anexample signal measured in a location even more remote from the NMESsite (region (2) of FIG. 3( e)) is shown. Though the same shape andpulse width as the signal shown in (b), this signal measured more remotefrom the region of stimulation has relatively lower amplitude.

One embodiment of the presently-disclosed devices, systems and methodsoperates by producing the inverted version of the signal shown in FIG.3( c) and delivering it to the body at an appropriate location (forexample, near region (2) of FIG. 3( e)). We refer to this invertedsignal as the counter signal, an example of which is shown in FIG. 3(d). By producing an opposite polarity but equal amplitude counter signalusing counter signal electrodes (303), it is possible to cancel out theinterference signal originating from the stimulation region (region ofelectrodes (302)) and prevent it from spreading into more distalregions. Counter signal characteristics may be matched so that thepropagation characteristics of the counter signal are similar to thoseof the NMES interference signal, allowing for the impact of theinterference signal to be minimized over considerable distances.

The amplitude of the counter signal is important to note. As describedabove, to be practical any counter signal needs to minimize the effectof the NMES interference signal on remote monitoring and/or sensingdevices, but also not meaningfully impact the effectiveness of the NMESitself. Since in general counter signals are required to be ofrelatively small amplitude (especially relative to stimulation signals,for example that shown FIG. 3( a)), they do not significantly interactwith muscles or cancel out the electrical current that needs to bedeposited in the muscle region in order to provide suitable NMEStherapy.

Preferable embodiments will use fixed positions of the stimulationelectrodes and counter-signal producing electrodes. As such, empiricalinformation may be used to determine a priori the most suitable countersignal for the control unit to deliver in order to most effectivelycancel the NMES interference signal in remote regions. In variousembodiments, this counter signal may be static, may be adjusted asneeded based upon adjustments (ex. intensity, pulse width) to the signalbeing delivered to the stimulation electrodes for NMES, and/or may becalculated based on local factors such as control unit-measuredimpedance between either or both sets of electrodes. In someembodiments, the counter signal may be adjusted or fine-tuned manuallyby an operator, for example by an operator who is observing an ECGmonitor and may adjust the counter signal such that use of the NMESdevice produces the least amount of interference.

In variations of the preferable embodiments, sensor systems may be usedto measure the interference signal as it travels away from the regionbeing treated with NMES. In these embodiments, one or more sensors canbe utilized to help the control unit produce the most effective countersignal possible. Sensors may be utilized in a number of ways. In someembodiments, the sensors may be positioned to measure the interferencesignal (as in FIG. 4( a)), which can then be inverted and possiblyscaled to produce a counter signal. In variation implementations, asensor could be placed in a region distal to the electrodes used todeliver the counter signal (for example, as shown in FIG. 4( c)), andthus be positioned to measure any residual signal. Some implementationsmay use multiple sensors in one or both of these positions, or in otherpositions that will be clear to those skilled in the art. Depending onthe embodiment, sensors may be built into a pad with the electrodes(fixing their relative positions), or may be placed discretely on thesubject without the use of a pad. In some embodiments, multiple pads maybe utilized to optimize the position of sensors and electrodes.Depending on the body part receiving NMES and the relative position ofthe monitoring equipment and/or device sensors where interference isintended to be minimized, sensors and counter signal electrodes may beplaced in close proximity to the stimulation region (for example, as inFIG. 4( b)) or more remotely from the stimulation region (as in FIG. 4(e)).

In some embodiments it may be desirable to minimize interference withmore than one electrical sensor remote from the NMES site. For example,when using NMES in the presence of ECG monitoring, which requiresmultiple electrodes. In this situation, some embodiments may use simpleconfigurations of counter signal producing electrodes (ex. FIG. 5( a)),while other embodiments will implement more advanced active cancellationtechniques that account for different path lengths and directionality ofthe interference signal as it spreads away from the region of NMES. Anexample configuration of a more advanced active cancellation system(control unit not shown) is shown in FIG. 5( b).

In a preferable embodiment of the method described herein, one stepwould involve placing at least one stimulation electrode and at leastone counter-signal producing electrode on the body of a subject. A laterstep would be applying stimulation energy to a body region of a subject,with sufficient enough amplitude to produce a muscle contraction. Asimultaneous (or slightly later, depending on the configuration) step inthe method is to apply a second active signal to the body, in the formof a counter signal, said counter signal having an appropriate shape,polarity, amplitude, and anatomical origin to effectively minimize oreliminate the interference the first stimulation energy signal producesin electrical measurements captured by sensors remote to the NMESregion. In some embodiments of the method, an additional step involvesusing a sensor to estimate either the interference signal, the residualsignal resulting after the counter signal is applied, or both, andadjusting the counter and/or NMES signal properties accordingly in orderto minimize electrical interference with remote monitoring equipmentand/or devices that require electrical sensing to function properly. Anexample embodiment of the method is shown in FIG. 6.

DESCRIPTION OF THE DRAWINGS

While preferable embodiments of the invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention.

As shown in FIG. 1, example preferable embodiments of thepresently-disclosed devices and systems. In 1(a), control unit 101contains an LCD touchscreen display/user interface as well as a numberof controls, knobs, buttons, and dials. An interconnect cable 102connects the control unit to pads 103 that contain both stimulation andcounter signal electrodes. In 1(b), the subject-contacting side of pad103 is shown, with an example configuration of stimulation 104 andcounter signal producing 105 electrodes.

As shown in FIG. 2, variations of preferable embodiments of the devicesand systems that include electrodes used to deliver NMES and electrodesused to produce a counter signal. In 2(a), a subject 201 is beingmonitored with four ECG electrodes 204 on his torso. A control unit 202is connected to a pad 203 configured to provide NMES and counter signalsto the leg. In (b), the pad 203 is configured so that counter signalelectrodes 205 are located between stimulation electrodes 2044 and ECGmonitoring sensor electrodes 204 (not shown in the FIG. 2( b)) when pad203 is placed on the subject as shown in FIG. 2( a). In (c), shown is adifferent shaped pad 206 configured for another body part of thesubject. In the embodiment shown, a different relative position of thecounter signal electrodes 205 and stimulation electrodes 2044 isimplemented. In (d), an embodiment that does not use a pad and insteaduses discrete individual electrodes that can be placed on the subject inpositions that the NMES operator deems appropriate is shown.

As shown in FIG. 3 various electrical signals associated with thedevices, systems, and methods described herein. In all sub-figures, they-axis represents relative voltage (not to scale) and the x-axisrepresents time (not to scale). All signals shown are approximate andfor the purpose of example only. Please refer to (e) for clarificationas the signals in sub-figures (a)-(d) are described. In (a), an examplesignal that a control unit 301 may provide to stimulation electrodes302. In (b), an example signal that could be measured outside of theregion of stimulation at location (1). In (c), a relatively smalleramplitude signal that could be measured further outside the region ofstimulation at location (2). The signals shown in (b) and (c) are theinterference signal that is produced as a byproduct of NMES signal (a)being applied in the intended region of stimulation. In (d), an examplecounter signal with similar amplitude but opposite polarity of theinterference signal shown in (c), which can be applied at counter signalelectrodes 303 to cancel out the interference signal and thus minimizethe impact it could have on monitoring sensors and/or devices locatedmore remotely to the region of NMES. In (e), an example systemconfiguration, as well as annotated regions (1) and (2) that correspondto the signals shown in (b) and (c), respectively.

As shown in FIG. 4, variations of preferable embodiments of the devicesand systems that include electrodes used to deliver NMES and electrodesused to produce a counter signal as well as sensors used in conjunctionwith the system. In (a), a system pad 401 contains a sensor 403 that islocated between stimulation electrodes 402 and counter signal electrodes404. In (b), a variation embodiment that uses multiple sensors 403. In(c), a further variation embodiment where the sensor 403 is positionedrelatively further away from the zone of stimulation compared to thelocation of the counter signal electrodes 404. In (d), an embodimentthat uses two system pads, a primary pad 401 that contains stimulationelectrodes 402 and a secondary pad 405 that contains both a sensor 403and a monopolar counter signal electrode 404. In (e), an embodiment ofthe systems and devices configured for use on the arm of a subject. Boththe sensors 403 and the counter signal electrodes 404 are located in aposition remote from the zone of stimulation.

As shown in FIG. 5, variation embodiments of the devices and systemshown in multiple configurations. In (a), a system pad 502 is placed ona subject's leg, with counter signal producing sensors 503 located onthe system pad in a region proximal to the zone of NMES but remote fromthe ECG sensors 501. A variation embodiment is shown in (b), where pad502 contains only stimulation electrodes, and counter signal producingelectrodes 503 are positioned relatively more remotely from the NMESsite, closer to the monitoring sensors where it is desired to minimizeany interference signal originating from the stimulation zone. In (b),several sets of counter signal producing electrodes are used to accountfor various directionality aspects of the interference signal as ittravels to different ECG sensors 501.

As shown in FIG. 6, steps in one preferable embodiment of the methoddescribed herein. Shown are several example steps in a preferableembodiment of the method disclosed. Variations of this preferable methodmay skip the sensing step (b), relying on operator-set,internally-calculated, or pre-determined settings for the countersignal.

1. A muscle stimulation system comprising a stimulation electrodeconfigured to be secured to a patient to deliver an electrical musclestimulation signal to the patient; an counter signal electrodeconfigured to be secured to the patient and relative to the stimulationelectrode to deliver an electrical counter signal to the patient; and atleast one controller adapted to generate the electrical musclestimulation signal and the counter signal, wherein the electricalcounter signal is adapted to destructively interfere with an electricalinterference signal resulting from the electrical muscle stimulationsignal.
 2. The system of claim 1 wherein the electrical counter signalis adapted such that it does not degrade the stimulating effect of theelectrical muscle stimulation signal.
 3. The system of claim 1 whereinthe electrical counter signal is adapted to minimize or eliminate theinterference signal.
 4. The system of claim 1 wherein the electricalcounter signal has an opposite polarity and substantially the sameamplitude as the interference signal.
 5. The system of claim 1 whereinthe electrical counter signal has an amplitude that is less than anamplitude of the electrical muscle stimulation signal.
 6. The system ofclaim 1 wherein the electrical counter signal has a shape that isdifferent than a shape of the electrical muscle stimulation signal. 7.The system of claim 1 wherein the at least one controller is adapted sothat the electrical counter signal is fixed.
 8. The system of claim 1wherein the at least one controller is adapted such that the electricalcounter signal can be manually or automatically varied.
 9. The system ofclaim 8 wherein the at least one controller is adapted such that atleast one of an amplitude, a phase, and a shape of the electricalcounter signal can be manually or automatically varied.
 10. The systemof claim 8 wherein the at least one controller is adapted to vary theelectrical counter signal based on the electrical interference signal.11. The system of claim 10 further comprising an interference signalsensor configured to be secured to the patient and to sense theelectrical interference signal.
 12. The system of claim 1 furthercomprising an interference sensor configured to be secured to thepatient and adapted to sense the interference signal at a locationdifferent than where the electrical muscle stimulation signal isdelivered to the patient, wherein the electrical counter signal is basedon the sensed interference signal.
 13. The system of claim 1 wherein theelectrical counter signal is adapted to reduce interference between asensed physiological signal from the patient and the interferencesignal.
 14. The system of claim 13 wherein the physiological signal fromthe patient is an EKG signal.
 15. The system of claim 1 furthercomprising a pad configured to be positioned on the patient andcomprising the stimulation electrode and the counter signal electrode.16. The system of claim 15 wherein the pad further comprises aninterference sensor adapted to sense the electrical interference signal.17. The system of claim 16 wherein the interference sensor is disposedbetween the stimulation electrode and the counter electrode.
 18. Thesystem of claim 16 wherein the counter electrode is disposed between thestimulation electrode and the interference sensor.
 19. A method ofreducing interference in a muscle stimulation system comprisingdelivering an electrical muscle stimulation signal to a patient tostimulate muscle contraction; and delivering an electrical countersignal to the patient that destructively interferes with an interferencesignal resulting from delivering the electrical muscle stimulationsignal.
 20. The method of claim 19 wherein delivering the electricalcounter signal does not degrade the stimulating effect of the deliveredelectrical muscle stimulation signal.
 21. The method of claim 19 whereindelivering the electrical counter signal minimizes or eliminates theinterference signal.
 22. The method of claim 19 wherein delivering theelectrical counter signal comprises delivering an electrical countersignal that has an opposite polarity and substantially the sameamplitude as the interference signal.
 23. The method of claim 22 whereindelivering the electrical counter signal comprises delivering anelectrical counter signal that has an amplitude less than an amplitudeof the delivered electrical stimulation signal.
 24. The method of claim19 wherein delivering the electrical counter signal comprises deliveringan electrical counter signal that has a shape that is different than ashape of the electrical muscle stimulation signal.
 25. The method ofclaim 19 wherein the method further comprises modifying a parameter ofthe delivered electrical counter signal and delivering a secondelectrical counter signal with the modified parameter.
 26. The method ofclaim 25 wherein modifying a parameter of the delivered electricalcounter signal comprises modifying at least one of an amplitude, aphase, and a shape of the delivered electrical counter signal.
 27. Themethod of claim 25 wherein modifying a parameter of the deliveredelectrical counter signal is in response to sensing the interferencesignal with an interference signal sensor.
 28. The method of claim 19further comprising sensing the interference signal with an interferencesignal sensor.
 29. The method of claim 28 wherein sensing theinterference signal with an interference signal sensor comprises sensingthe interference signal at a location different than where the musclestimulation signal is delivered to the patient and where the countersignal is delivered to the patient.
 30. The method of claim 28 whereinsensing the interference signal with an interference signal sensorcomprises sensing the interference signal at a location between wherethe muscle stimulation signal is delivered to the patient and where thecounter signal is delivered to the patient.
 31. The method of claim 19wherein delivering an electrical counter signal is in response tosensing the interference signal.
 32. The method of claim 19 furthercomprising sensing a physiological signal from the patient, and whereindelivering the counter signal reduces interference between the sensedphysiological signal and the interference signal.
 33. The method ofclaim 32 wherein sensing a physiological signal from the patientcomprises sensing an EKG signal from the patient, and delivering thecounter signal reduces interference between the EKG signal and theinterference signal.